1. Field of the Invention
The present invention relates to engine starters for internal combustion engines and more particularly to starters of the positive shift type which include a dentil clutch to provide driving and overrunning functions and more specifically a centrifugal separator for effecting the automatic separation of the dentil clutch teeth after the engine becomes self-running to prevent torque transmission in the overspeed or overrunning condition.
2. Description of the Prior Art
As is well known in the prior art, an engine starter normally includes a starter motor, a drive pinion slidably mounted on an output shaft thereof for meshing engagement with the ring gear of an engine. In addition, the starter has an overrunning clutch to permit the engine to start and accelerate under its own power without driving the starter motor shaft at excessive speeds. The purpose of the overrunning clutch is to break the driving connection between the drive pinion and the starter motor. The overrunning clutch thus prevents abuse by extended periods of overrun at high speeds when the attendant neglects to disengage the starter after the engine has become self-running, thereby causing the engine to drive the starter motor.
In some prior art starters, for example, U.S. Pat. No. 3,263,509, owned by the assignee of the present patent application, centrifugal separators of the type using arcuate flyweight members annularly arranged have been used to effectuate separation of the dentil teeth upon occurrence of an overrunning condition. A centrifugal separator of this type has resulted in manufacturing problems during assembly due to the fact that the arcuate flyweight elements must be held in position through the use of grease lubricant while the various other details of the starter are assembled. This has resulted in a time consuming process to assemble the arcuate flyweight members within the starter mechanism. In addition, in operation, the frictional forces between the inclined surfaces of the arcuate flyweight members and the inner inclined surface that these elements contact generate excessive localized heat upon long periods of overrunning of the clutch. This results in the arcuate flyweight members locking up against the inclined surface of the thrust washer making the separator ineffective. This causes excessive wear on the dentil teeth over a long period of time, thereby reducing the useful life of the starter gearing. In order to overcome this problem, larger flyweight members were required to cause separation of the clutch teeth so as to overcome the localized heat problem. Due to the physical size of the larger flyweight members, the use of this prior art design has been precluded in small drive applications.
A significant improvement was obtained in the useful life of prior art starters utilizing centrifugal separators characterized by a plurality of spherical weight members held by a biasing member. For example U.S. Pat. No. 3,915,020, owned by the assignee of the present patent application, and U.S. Pat. No. 4,114,746. In the prior art designs, a set of spherical centrifugal weights are mounted on radially flexible resilient arms which are held in rolling contact with a tapered angular guide surface to force the angular guide surface and hence the driving clutch member away from the driven clutch member. The spherical weights generate this centrifugal separating force as the spherical weights move radially outward when the speed of rotation of the engine overruns the starter shaft. These designs, however, require the use of larger spherical weights to cause separation of the clutch teeth when the speed of rotation exceeds a predetermined speed since the centrifugal force of the weights must overcome the spring force of the biasing arms before separation occurs. The use of larger spherical flyweights also precludes its use in small drive applications.
However, neither U.S. Pat. No. 3,915,020 nor U.S. Pat. No. 4,114,746 completely eliminated the difficult assembly techniques required to assemble the spherical weight members on the biasing arms into the starter gearing, nor have they reduced significantly the cost of assembling of the starter. Furthermore, none of the aforementioned prior art designs have been able to reduce the physical size of the separator members to permit the use of these designs in small drive applications.